1. Field of the Invention
The present invention relates to a sputtering apparatus having a magnet unit.
2. Description of the Related Art
A certain type of sputtering apparatus controls the plasma generation state on the discharge surface of a target using a magnet unit arranged on the back surface of a cathode electrode which supports the target (see Japanese Patent No. 02769572 and WO/2010/076862).
In an apparatus that uses a magnet unit, it is difficult to remove a target due to the presence of a force (an attractive force in many cases) acting between the magnet unit and the target in target replacement. Hence, the target is often replaced after the magnet unit is moved away from the target using, for example, a driving mechanism.
Also, Japanese Patent No. 2769572 and WO2010/076862 disclose apparatuses that perform, for example, control to move the magnet unit further away from the target in proportion to the time for which the target is used, thereby adjusting the magnetic flux density on the target surface even if this surface is eroded due to the long-term use of the target.
The sputtering apparatus as described above is also used in a process of manufacturing a device including a magnetic film, such as a magnetic head, a magnetic medium, or an MRAM device. However, in this case, a large number of lines of magnetic force generated by the magnet unit are shielded inside the magnetic target, thus making it difficult to obtain a magnetic flux density required for discharge on the target surface. To prevent this, in recent years, when a magnetic target is used, a magnet material having a high energy product is adopted as the magnet material used for the magnet unit.
Unfortunately, an attractive force as large as, for example, 6,000 N or more acts between the magnetic target and the magnet unit which produces such a strong magnetic force. The attractive force increases as the target is made thicker to improve the operating rate of a film forming apparatus.
In such a case, when the magnet unit is driven with the driving capacity of the conventional apparatus, it is possible to increase, for example, the reduction ratio between a motor and a rectilinear motion conversion mechanism, but this prolongs the process stop time. It is also possible to improve the rated power of a driving source. However, because the attractive force considerably changes even if the distance between the magnet unit and the magnetic target changes by only several millimeters, it is inefficient to match the rated power of the driving source with a maximum attractive force that acts between them.
Japanese Patent No. 02769572 and WO/2010/076862 propose no solution to the above-mentioned problem resulting from the presence of an attractive force acting between the magnet unit and the target or a backing plate formed by a magnetic material.